2,879 research outputs found
Pouchitis.
Pouchitis is a major long-term complication of the continent ileostomy as well as the ileoanal pouch anastomosis. When diagnosed on the basis of clinical, endoscopic and histologic features, this syndrome has been demonstrated almost exclusively in patients with ulcerative colitis. The clinical course, the endoscopic findings and the histologic abnormalities resemble those of ulcerative colitis. The association with extra-intestinal manifestations further supports the hypothesis that pouchitis represents ulcerative colitis in the small bowel. All ileal reservoirs show bacterial overgrowth, especially of anaerobes. As a response to this altered intraluminal environment chronic inflammation and incomplete colonic metaplasia occur. The efficiency of metronidazole does suggest that bacteriological factors play an important role in the pathogenesis of pouchitis
A cryogenic amplifier for fast real-time detection of single-electron tunneling
We employ a cryogenic High Electron Mobility Transistor (HEMT) amplifier to
increase the bandwidth of a charge detection setup with a quantum point contact
(QPC) charge sensor. The HEMT is operating at 1K and the circuit has a
bandwidth of 1 MHz. The noise contribution of the HEMT at high frequencies is
only a few times higher than that of the QPC shot noise. We use this setup to
monitor single-electron tunneling to and from an adjacent quantum dot and we
measure fluctuations in the dot occupation as short as 400 nanoseconds, 20
times faster than in previous work.Comment: 4 pages, 3 figure
ON NON-RIEMANNIAN PARALLEL TRANSPORT IN REGGE CALCULUS
We discuss the possibility of incorporating non-Riemannian parallel transport
into Regge calculus. It is shown that every Regge lattice is locally equivalent
to a space of constant curvature. Therefore well known-concepts of differential
geometry imply the definition of an arbitrary linear affine connection on a
Regge lattice.Comment: 12 pages, Plain-TEX, two figures (available from the author
Josephson squelch filter for quantum nanocircuits
We fabricated and tested a squelch circuit consisting of a copper powder
filter with an embedded Josephson junction connected to ground. For small
signals (squelch-ON), the small junction inductance attenuates strongly from DC
to at least 1 GHz, while for higher frequencies dissipation in the copper
powder increases the attenuation exponentially with frequency. For large
signals (squelch-OFF) the circuit behaves as a regular metal powder filter. The
measured ON/OFF ratio is larger than 50dB up to 50 MHz. This squelch can be
applied in low temperature measurement and control circuitry for quantum
nanostructures such as superconducting qubits and quantum dots.Comment: Corrected and completed references 6,7,8. Updated some minor details
in figure
Sparling two-forms, the conformal factor and the gravitational energy density of the teleparallel equivalent of general relativity
It has been shown recently that within the framework of the teleparallel
equivalent of general relativity (TEGR) it is possible to define the energy
density of the gravitational field. The TEGR amounts to an alternative
formulation of Einstein's general relativity, not to an alternative gravity
theory. The localizability of the gravitational energy has been investigated in
a number of space-times with distinct topologies, and the outcome of these
analises agree with previously known results regarding the exact expression of
the gravitational energy, and/or with the specific properties of the space-time
manifold. In this article we establish a relationship between the expression
for the gravitational energy density of the TEGR and the Sparling two-forms,
which are known to be closely connected with the gravitational energy. We also
show that our expression of energy yields the correct value of gravitational
mass contained in the conformal factor of the metric field.Comment: 12 pages, Latex file, no figures, to be published in Gen. Rel. Gra
On certain relationships between cosmological observables in the Einstein-Cartan gravity
We show that in the Einstein-Cartan gravity it is possible to obtain a
relation between Hubble's expansion and the global rotation (vorticity) of the
Universe. Gravitational coupling can be reduced to dimensionless quantity of
order unity, fixing the scalar mass density and the resulting negative
cosmological constant at spacelike infinity. Current estimates of the expansion
and rotation (see also astro-ph/9703082) of the Universe favour the massive
spinning particles as candidate particles for cold and hot dark matter. Nodland
and Ralston vorticity (Phys. Rev. Lett. 78 (1997) 3043) overestimates the value
favoured by the Einstein-Cartan gravity for three orders of magnitude.Comment: 7 pages, LaTeX styl
A risk evaluation of traces of packaging materials in former food products intended as feed materials
Space-time defects and teleparallelism
We consider the class of space-time defects investigated by Puntigam and
Soleng. These defects describe space-time dislocations and disclinations
(cosmic strings), and are in close correspondence to the actual defects that
arise in crystals and metals. It is known that in such materials dislocations
and disclinations require a small and large amount of energy, respectively, to
be created. The present analysis is carried out in the context of the
teleparallel equivalent of general relativity (TEGR). We evaluate the
gravitational energy of these space-time defects in the framework of the TEGR
and find that there is an analogy between defects in space-time and in
continuum material systems: the total gravitational energy of space-time
dislocations and disclinations (considered as idealized defects) is zero and
infinit, respectively.Comment: 22 pages, no figures, to appear in the Class. Quantum Gravit
Geodesic Deviation in Regge Calculus
Geodesic deviation is the most basic manifestation of the influence of
gravitational fields on matter. We investigate geodesic deviation within the
framework of Regge calculus, and compare the results with the continuous
formulation of general relativity on two different levels. We show that the
continuum and simplicial descriptions coincide when the cumulative effect of
the Regge contributions over an infinitesimal element of area is considered.
This comparison provides a quantitative relation between the curvature of the
continuous description and the deficit angles of Regge calculus. The results
presented might also be of help in developing generic ways of including matter
terms in the Regge equations.Comment: 9 pages. Latex 2e with 5 EPS figures. Submitted to CQ
Test Matter in a Spacetime with Nonmetricity
Examples in which spacetime might become non-Riemannian appear above Planck
energies in string theory or, in the very early universe, in the inflationary
model. The simplest such geometry is metric-affine geometry, in which {\it
nonmetricity} appears as a field strength, side by side with curvature and
torsion. In matter, the shear and dilation currents couple to nonmetricity, and
they are its sources. After reviewing the equations of motion and the Noether
identities, we study two recent vacuum solutions of the metric-affine gauge
theory of gravity. We then use the values of the nonmetricity in these
solutions to study the motion of the appropriate test-matter. As a
Regge-trajectory like hadronic excitation band, the test matter is endowed with
shear degrees of freedom and described by a world spinor.Comment: 14 pages, file in late
- …